Seal for a reciprocatory bar

ABSTRACT

A reciprocatory bar in a bore in a wall of a pressurized container has an annular peripheral groove receiving an annular non-return valve member allowing flow inwardly along the bore and forming part of a piston pump arrangement. The container wall has an annular peripheral groove opening into the bore and receiving an annular non-return valve member also allowing inward flow and forming part of the piston pump arrangement. An annular seal received in another annular peripheral groove in the container wall defines with the latter valve member, the bar and the wall a relieving chamber of the arrangement, of which a pump chamber is defined by the two valve members, the bar and the wall. On reciprocation of the bar, pressurized medium in the relieving chamber is returned to the interior of the container.

United States Patent [1 1 Hubschmann 1 June 4, 1974 1 SEAL FOR A RECIPROCATORY BAR [75] Inventor: Karl Wolfgang Hubschmann.

Langwe id, Germany [73] Assignee: Motoren-Werke Mannheim AG,

Mannheim, Germany [221 Filed: May 11, 1972 121] App]. No.: 252,287

[30] Foreign Application Priority Data May 11, 1971 Germany 2123140 152] U.S. Cl 417/511, 277/15, 277/144, 417/281, 417/550, 417/555 [51] Int. Cl. F041) 21/02 158] Field of Search 417/281, 439, 443,511, 417/513, 555; 92/192, 98; 277/15, 58, 143, 144

[56] References Cited UNITED STATES PATENTS 12/1968 Aronson 277/15 3,620,652 11/1971 Jaspers et a1. 11 417/550 X 3,667.348 6/1972 Neelen 92/83 FOREIGN PATENTS OR APPLICATIONS 1.247.7xu 8/1967 Germany 277/143 Germany 60/24 Great Britain 277/15 Primary E.\uminvrC. J. Husar Assistant Examiner-Leonard Smith Almrney, Agent, or FirmEriC H, Waters 1571 ABSTRACT A reciprocatory bar in a bore in a wall of a pressurized container has an annular peripheral groove receiving an annular non-retum valve member allowing flow inwardly along the bore and forming part of a piston pump arrangement. The container wall has an annular peripheral groove opening into the bore and receiving an annular non-return valve member also allowing inward flow and forming part of the piston pump arrangement. An annular seal received in another annular peripheral groove in the container wall defines with the latter valve member, the bar and the wall a relieving chamber of the arrangement, of which a pump chamber is defined by the two valve members,

the bar and the wall. On reciprocation of the bar, 1

pressurized medium in the relieving chamber is returned to the interior of the container.

5 Claims, 9 Drawing Figures PATENTEDJUH 4 I974 SHEET 3 0F 3 PEG. z

SEAL FOR A RECIPROCATORY BAR BACKGROUND OF THE INVENTION Field of the Invention The invention relates to a seal between a reciprocatory bar and a receiving wall of a fixed container for a pressurized medium.

Description of the Prior Art It is conventional to provide a seal between a reciprocating bar and a receiving wall of a fixed container, the interior of which contains a pressurized medium, the seal comprising at least one annular sealing element which tightly surrounds the bar and which is prevented almost completely by the container from participating in the reciprocation of the bar.

This conventional seal operates satisfactorily at high pressure differentials only when a plurality of sealing elements are fitted one behind the other, and this results in a system of considerable length. Seals not operating on the above-described principle, e.g., a seal consisting of a diaphragm bellows, require to be supported by an incompressible fluid when the pressure differentials are high, the pressure of the fluid needing to be increased as the pressure of the medium increases, and thus to be regulated. This arrangement is complicated and expensive.

SUMMARY OF THE INVENTION According to the present invention, there is provided in combination, a container for containing a pressurized medium in its interior, a bore through a wall of said container, a bar extending through said bore longitudinally thereof and reciprocable longitudinally thereof, annular sealing means encircling said bar and interposed sealingly between said bar and said wall, and piston pump means including portions of said bar and said wall and arranged to return to said container pressurized medium penetrating said bore to a location immediately adjacent to and inwards of said annular sealing means.

As long as the bar is moving, the piston pump means can practically eliminate anypressure differential acting on the sealing means, so that asingle sealing element suffices for the sealing means.

The bar and the wall are enabled to operate as a piston pump in a simple and therefore advantageous manner by the provision of a first annular valve member,

which is located between the interior of the container and the sealing element and which is prevented almost completely by the housing from participating in the reciprocation of the bar and tightly surrounds the bar, and prevents the'medium fromv flowing from the interior of the container towards the sealing element but permits flow in the opposite direction, and a second annular valve member, which is provided on the bar and participates almost completely in the reciprocation of the bar and the stroke of which is substantially equal to the distance between the first valve member and the sealing element, the second valve member bearing tightly against the wall of the container to effect a seal and preventing the medium from flowing from the interior of the container towards the sealing element, but permitting flow in the opposite direction.

In this way, there are formed a pump chamber, defined by the two valve members, and the peripheries of the bar and the bore, and a relieving chamber, defined by the second valve member, the sealing element, and the peripheries of the bar and the bore, the volumes of which chambers alternately increase and diminish as a result of the movement of the bar, so that the medium is returned from the relieving chamber to the pump chamber and thence to the interior of the container.

To prevent sub-atmospheric pressure from occurring in the relieving chamber as could cause the .entry therein of air from the surrounding atmosphere, the pump chamber and the relieving chamber are advantageously interconnected through a cut-off element which is open when the pressure in the relieving chamber is below a predetermined value, but which is otherwise closed. In this way, the relieving chamber is topped up again to a nominal pressure when this becomes necessary.

When the bar is stationary, the aforedescribed pumping action ceases, and the relieving chamber is filled with pressurized medium from the interior of the container by way of the unavoidable small zones where sealing is incomplete. In order to prevent the medium from escaping by way of the sealing element which is now subjected to the entire differential pressure, this element advantageously has provided adjacent thereto a flexible part which does not touch the periphery of the bar when the relieving chamber is not under pressure, but which is pressed tightly on to the circumference of the bar when the relieving chamber-is pressurized and by the pressure obtaining therein.

For this purpose, the sealing element is advantageously formed as an annular piston which has a frustoconical outer end face widening towards the flexible part and co-operating with a substantially complementary inner end face of the flexible part to press the latter on to the periphery of the bar.

For this purpose, the flexible part advantageously consists of a ring which, together with the sealing element, is positioned in an annular groove in the container wall and the cross-section of which is substantially in the form of a right-angled triangle, the rightangle of which is presented to the bar and to that side wall of the groove further from the interior of the container, at least that corner of the triangle nearest to the interior of the container being deformable by the sealing element.

In an alternative arrangement, the sealing element consists of a ring of rectangular cross-section which is loosely received in an annular groove in the container wall and bears tightly against both the bar and one of the side-walls of the groove. The sealing effect is achieved by the ring being tightly pressed against that side-wall of the groove further from the container interior by the axial force resulting from the pressure differential, the latter also acting on the outer peripheral face of the ring and pressing the latter tightly on to the bar.

In a preferred arrangement, the first valve member consists of a ring of rectangular cross-section which is received loosely in an annular groove in the container wall and which, in a manner known per se from French Patent Specification No. 1,193,072, contains recesses in that of its end faces directed towards the interior of the container. When the pressure of the medium in the interior of the container is greater than in the pump chamber, that end face of the first valve member presented to the pump chamber is caused to bear tightly against the corresponding side wall of the groove by the pressure differential. This situation occurs when the bar moves away from the interior of the container, so that the friction force of the bar on the ring is applied in the same direction as is the differential pressure. At the same time, the pressure in the interior of the container becomes effective and flows over the recessed end face of the ring into the gap between the base of the groove and on to the outer peripheral face of the first valve member, pressing the latter tightly on to the bar. When the pressure in the pump chamber is greater than that in the interior of the container, that end face of the first valve member that is presented to the pump chamber is lifted from the corresponding side-wall of the groove by the pressure differential. This situation occurs when the bar moves towards the interior of the container, so that the friction force of the bar on the ring is applied in the same direction as is the pressure differential. The first valve member is thus applied by that of its recessed end face to the corresponding sidewall of the groove, and the medium is displaced from the pump chamber over the lifted end face, through the gap between the outer peripheral face of the ring and the base of the groove, through the recesses and into the interior of the container. The first valve member thus operates in the manner of a pressure valve of a piston pump.

In a preferred arrangement, the second valve member consists of a ring of rectangular cross-section which is loosely received in an annular groove in the bar and which, in a manner known per se from French Patent Specification No. l,l93,072, contains recesses in that of its end faces directed towards the interior of the container. When the pressure of the medium in the pump chamber is greater than in-the relieving chamber, that end face of the second valve member that is presented to the relieving chamber is caused to bear tightly against the corresponding side-wall of the groove by the pressure differential. This situation occurs when the bar moves towards the interior of the container, so that the friction force of the container wall on the ring is applied in the same direction as is the'pressure differential. Atthe same time the pressure in the pump chamber becomes effective and the medium, flowsover the recessed end face of the ring, and into the gap between the base of the groove and the ring, on to' the inner peripheral face of the second valve member, pressing this member tightly against the wall. When the pressure in the relieving chamber is higher than in the pump chamber, then that end face of the second valve member that is presented to the relieving chamber is lifted from the corresponding side-wall of the groove by the pressure differential. This situation occurs when the bar moves away from the interior of the container, so that the friction force of the container wall on the ring is applied in the same direction as is the pressure differential. The

second valve member is thus applied by its recessed end face to the corresponding side-wall of the groove, and the medium is displaced from the relieving chamber over the lifted face, through the gap between the inner peripheral face of the ring and the base of the groove, through the recesses and into the pump chamber. The second valve member thus acts in the manner of an inlet valve of a piston pump.

The sealing element and the valve members are advantageously not slit, so as to prevent the risk of leakage at the abutting faces at the slits. The bias at the cylindrical sealing face that is necessary for effecting a seal is expediently achieved by the unstressed diameter of the sealing face of the element or valve member differing from that of the co-operating face of the bar or the wall to an extent such'that the sealing face is mechanically urged on to the cooperating face when fitted thereon or therein.

If limited amounts of leakage can be accepted, the sealing element and the valve members can be slit, and the cylindrical sealing face can be caused to bear against the co-operating face both by the inherent resilience of the ringand by a clamping ring.

Particularly in the case of the unslit form with an oversize fit at the sealing face, but also in the case of the slit form of sealing element or valve member, the ring may be advantageously made of a deformable material and preferably of plastics.

If the medium to be sealed off does not permit the presence of a lubricant, the ring may advantageously be made of a material having self-lubricating properties.

The sealing element and the valve members may also take the form of lip seals, and the inner faces of the lips may be directed towards the interior of the container in order to ensure that the sealing and valve actions are achieved in the required manner.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an axial sectional view of a seal between a reciprocatory bar and a container wall receiving the bar.

FIG. 2 is a view similar to FIG. -I, but also showing a manner of providing a cut-off element to prevent the occurrence of sub-atmospheric pressure in a relieving chamber.

FIG. 3 is a view similar to FIG. 1, but showing a modified version of the seal.

FIG. 4is a cross-sectional view of a first annular valve member of. the seal slit in the manner of a piston ring known per se. 7

FIG. 5 is'a cross-sectional view of the first annular valve member but having a clamping ring.

FIG. 6 is a top plan half view of the member and the ring shown in FIG. 5. I

FIG. 7 is a cross-sectional viewof a second annular valve member of the seal slit in the manner of a piston ring known per se- FIG. 8 is a cross-sectional view of the second annular valve member but having a clamping ring.

FIG. 9 is a top plan half view of the member and the ring shown in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The seal illustrated in FIG. 1 is used for sealing off the gap between a bar I and a container wall 2'in a bore of which the bar 1 reciprocates axially. A first annular valve member 3 separates the interior 4- of the container, containing a pressurized medium, from a pump chamber 5. A second annular valve member 6 which reciprocates with the bar 1 separates the pump chamber 5 from a relieving chamber 7. The volumes of the chambers 5 and 7 increase and diminish alternately and periodically as a result of the reciprocation of the bar. The valve members 3 and 6 provide seals in one direction only, namely from the interior 4 to the chamber 5, and from the chamber 5 to the chamber 7.

Between an outer space 8, communicating with the ambient atmosphere, and the relieving chamber 7 there is fitted a sealing element 9 which constitutes the actual seal. To ensure that the smallest possible pressure differential acts on the sealing element 9, any leakages of 5 pressurized medium from the interior 4 into the chambers 5 and 7 are returned to the interior 4 by the reciprocatory action of the bar 1. When this happens. the valve member 3 operates as a pressure valve, and the valve mernber 6 as a suction valve or piston ring of a piston pump. To prevent sub-atmospheric pressure from arising in the chamber 7, this chamber and the chamber 5 can be inter-connected through a cut-off el-' ement 10, as illustrated in FIG. 2. The cut-off element is opened by a spring-loaded diaphragm I I when the absolute pressure in the chamber 7 falls below a predetermined value which can be adjusted by varying the bias of a spring 12. When the bar 1 stops reciprocating, the above-described pumping action ceases, and the chambers 5 and 7 become filled with pressurized medium from the interior 4 through the unavoidable small incompletely sealed zones in the valve members 3 and 6, so that in this case the full pressure differential is applied to the sealing element 9, and this could lead to fairly great medium losses in the inoperative condition. The arrangement illustrated in FIG. 3 avoids this disadvantage. In this arrangement, the sealing element 9 is sealed off at its outer peripheral face with the aid of an O-ring l3, and has an axially outwardly widening frusto-conical end face which co-operates with a similar end face on a flexible annular part 14. As a result of the high pressure in the chamber 7 in the inoperative condition, the sealing element is pressed axially outwardly and alters the shape of the part 14 from that shown in the left-hand half of FIG. 3 to that shown in the righthand half of FIG. 3, in which form the apex of the triangular cross-section of the part 14 is pressed tightly on to the circumference of the bar 1. When the bar operates again, the pressurized medium from the chamber 7 is returned by way of the chamber 5 into the interior 4, so that the pressure in the chamber 7 drops. The part 14 then resumes the cross-sectional form shown in the left-hand half of FIG. 3. Instead of the O-ring 13, a diaphragm can be used for sealing the gap between the sealing element 9 and the wall 2.

The first annular valve member 3 shown in FIG. 4 is slit like a piston ring. The free ends at the slit 17 overlap each other. The member 3 as per FIG. 4 is resilient and its inner periphery l8 bears tightly on the bar 1 under the action of its own resilience. In this state which is shown in FIG. 4 the slit 17 is not fully closed, as illustrated. The upper face of the member 3 is provided with radial recesses 19 in order to obtain the effect of a nonreturn valve. The sealing element 9 can be of the same construction as the member 3 shown in FIG. 4 but without the radial recesses 19. FIGS. 5 and 6 show the first annular valve member 3 having the same shape as the member shown in FIG. 4 but insufficient resilience to obtain a tight bearing of the inner periphery 18 on the bar 1. This will particularly be the case when the member 3 is made of deformable plastics or self-lubricating material. Therefore a clamping ring 20 of strong resilient material is provided in order to obtain a sufficiently tight bearing of the inner periphery 18 on the bar 1. The sealing element 9 can be of the same construction as the member shown in FIGS. 5 and 6 but without the radial recesses 19. The second annular valve member 6 shown in FIG. 7 is slit like a piston ring. The free ends forming the slit 21 overlap each other. The member 6 as per FIG. 7 is resilient and its outer periphery 22 bears tightly on the wall 2 under the action of its own resilience. In this state which is shown in FIG. 7 the slit 21 is not fully closed. The upper face of the member 6 is provided with radial recesses 23 in order to obtain the effect of a nonreturn valve. FIGS. 8 and 9 show the second annular valve member 6 having the same shape as the member 6 shown in FIG. 7 but insufficient resilience to obtain a tight bearing of the outer periphery 22 on the wall 2. This will particularly be the case when the member 6 is made of deformable plastic or self-lubricating material. Therefore a clamping ring 24 of strong resilient material is provided in order to obtain a sufficiently tight bearing of the outer periphery 22 on the wall 2.

I claim:

1. In combination, a container for containing a pressurized medium in its interior, a bore through a wall of said container, a bar extending through said bore longitudinally thereof and reciprocable longitudinally thereof, annular sealing means encircling said bar and interposed sealingly between said bar and said wall, and piston pump means disposed inwards of said annular sealing means with respect to said interior and arranged to return to said container pressurized medium penetrating said bore to a location immediately adjacent to and inwards of said annular sealing means, said piston pump means comprising portions of said bar and said wall, a first annular non-return valve member of rectangular cross-section which closely encircles said bar, extends in said bore, is situated between said interior and said sealing means, is slit in the manner of a piston ring. and is formed with recesses in an annular face thereof directed towards said interior, a second annular nonreturn valve member which encircles said bar, bears sealingly against said wall in said bore, is situated between said interior and said sealing means, and moves with said bar on reciprocation of said bar relative to said wall, an annular groove formed in said wall coaxially with said bore, opening into said bore, and loosely receiving said first annular non-return valve member and thereby allowing said first annular nonreturn valve member to perform a small limited reciprocatory movement along said bore relative to said wall but otherwise preventing reciprocation of said first annular non-return valve member on reciprocation of said bar relative to said wall, and means allowing said second annular non-retum valve member to perform a small limited reciprocatory movement along said bar relative to said bar but otherwise ensuring that said second annular non-return valve member reciprocates with said bar, each of the first and second annular nonreturn valve members serving to prevent the medium from flowing in the direction from said interior towards said sealing means but to permit flow in the opposite direction.

2. In combination, a container for containing a pressurized medium in its interior, a bore through a wall of said container, a bar extending through said bore longitudinally thereof and reciprocable longitudinally thereof, annular sealing means encircling said bar and interposed sealingly between said bar and said wall, and piston pump means disposed inwards of said annular sealing means with respect to said interior and arranged to return to said container pressurized medium peneannular face thereof directed towards said interior, a

second annular non-return valve member which encircles said bar, bears sealingly against said wall in said bore, is situated between said interior and said sealing means, and moves with said bar on reciprocation of said bar relative to said wall, an annular groove formed in said wall co-axially with said bore, opening into said bore, and loosely receiving said first annular non-return valve member and thereby allowing said first annular non-return valve member to perform a small limited reciprocatory movement along said bore relative to said wall but otherwise preventing reciprocation of said first annular non-return valve member on reciprocation of said bar relative to said wall, means allowing said sec: ond annular non-return valve member to perform a small limited reciprocatory movement along said bar relative to said bar but otherwise ensuring that said second annular non-return valve member reciprocates with said bar, and clamping means pressing the inner periphery of said first annular non-return valve member against said bar, each of the first and second annular non-return valve members serving to prevent the medium from flowing in the direction from said interior towards said sealing means but to permit flow in the opposite direction.

3. In combination, a container for containing a pressurized medium in its interior, a bore through a wall of said container, a bar extending through said bore longitudinally thereof and reciprocable longitudinally thereof, annular sealing means encircling said bar and interposed sealingly between said bar and said wall, and piston pump means disposed inwards of said annular sealing means with respect to said interior and arranged to return to said container pressurized medium penetrating said bore to a location immediately adjacent to and inwards of said annular sealing means, said piston pump means c'omprisingfportionsof said bar and-said wall, a first annular non-return valve memberwhich closely encircles said bar, extends in said bore, is situated between said interior and said sealing means and is substantially stationary with respect to said wall on reciprocation of said bar relative to said wall, a second annular non-return valve member of rectangular crosssection which encircles said bar, bears sealingly against said wall in said bore, is situated between said interior and said sealing means, is slit in the manner of a piston ring, and is formed with recesses in an annular face thereof directed towards said interior, means allowing said first annular non-return valve member to perform a small limited reciprocatory movement along said bore relative to said wall but otherwise preventing reciprocation of said first annular non-return valve member on reciprocation of said bar relative to said wall, and an annular groove formed in said bar co-axially with said bore opening into said bore, and loosely receiving said second annular non-return valve member and thereby allowing said second annular non-return valve member to perform a small limited reciprocatory movement along said bar relative to said bar but otherwise ensuring that said second annular non-return valve member reciprocates with said bar, each of the first and second annular non-return valve members serving to prevent the medium from flowing in the direction from said interior towards said sealing means but to permit flow in the opposite direction.

4. In combination, a container for containing a pressurized medium in its interior, a bore through a wall of said container, a bar extending through said bore longitudinally thereof and reciprocable longitudinally thereof, annular sealing means encircling said bar and interposed sealingly between said bar and said wall, and piston pump means disposed inwards of said annular sealing means with respect to said interiorand arranged to return to said container pressurized medium penetrating said bore to a location immediately adjacent to an inwards of said annular sealing means, said piston pump means comprising portions of said bar and said wall, a first annular non-return valve member which closely encircles said bar, extends in said bore, is situated between said interior and said sealing means and is substantially stationary with respect to said wall on reciprocation of said bar relative to said wall, a second annular non-return valve member of rectangular crosssection which encircles said bar, bears sealingly against said wall in said bore, is situated between said interior and said sealing means, and is formed with recesses in an annular face thereof directed towards said interior, means allowing said first annular non-return valve member to perform a small limited reciprocatory movement along said bore relative to said wall but otherwise preventing reciprocation of said first annular non-return valve member on reciprocation of said bar relative to said wall, an annular groove formed in said bar co-axially with said bore, opening into said bore, and loosely receiving said second annular non-return valve member and thereby allowing said second annular non-return valve member to perform a small limited reciprocatory movement along said bar relative to said bar but otherwise ensuring that said second annular non-return valve member reciprocates with said bar, and clamping means pressing the outer periphery of said second annular non-return valve member against said wall, each of the first and second annular nonreturn valve members serving to prevent the medium from flowing in the direction from said interior towards said sealing means'but to permit flow in the opposite direction.

5. In combination, a container for containing a pressurized medium in its interior, a bore through a wall of said container, an annular groove formed in said wall co-axially with said bore and opening into said bore, a bar extending through said bore longitudinally thereof and reciprocable longitudinally thereof, a rectangular cross-section sealing ring which encircles said bar, is interposed sealingly between said bar and said wall, is loosely received in said groove, and bears against said bar and one of the side walls of the groove, clamping means pressing the inner periphery of said ring against said bar, and piston pump means disposed inwards of said annular sealing means with respect to said interior and arranged to return to said container pressurized medium penetrating said bore to a location immediately adjacent to and inwards of said annular sealing means, said piston pump means comprising portions of said bar and said wall, a first annular non-return valve member which closely encircles said bar, extends in said bore, is situated between, said interior and said cation of said bar relative to said wall, each of the first and second annular non-return valve members serving to prevent the medium from flowing in the direction from said interior towards said sealing means but to permit flow in the opposite direction. 

1. In combination, a container for containing a pressurized medium in its interior, a bore through a wall of said container, a bar extending through said bore longitudinally thereof and reciprocable longitudinally thereof, annular sealing means encircling said bar and interposed sealingly between said bar and said wall, and piston pump means disposed inwards of said annular sealing means with respect to said interior and arranged to return to said container pressurized medium penetrating said bore to a location immediately adjacent to and inwards of said annular sealing means, said piston pump means comprising portions of said bar and said wall, a first annular non-return valvE member of rectangular cross-section which closely encircles said bar, extends in said bore, is situated between said interior and said sealing means, is slit in the manner of a piston ring, and is formed with recesses in an annular face thereof directed towards said interior, a second annular non-return valve member which encircles said bar, bears sealingly against said wall in said bore, is situated between said interior and said sealing means, and moves with said bar on reciprocation of said bar relative to said wall, an annular groove formed in said wall co-axially with said bore, opening into said bore, and loosely receiving said first annular non-return valve member and thereby allowing said first annular non-return valve member to perform a small limited reciprocatory movement along said bore relative to said wall but otherwise preventing reciprocation of said first annular nonreturn valve member on reciprocation of said bar relative to said wall, and means allowing said second annular non-return valve member to perform a small limited reciprocatory movement along said bar relative to said bar but otherwise ensuring that said second annular non-return valve member reciprocates with said bar, each of the first and second annular non-return valve members serving to prevent the medium from flowing in the direction from said interior towards said sealing means but to permit flow in the opposite direction.
 2. In combination, a container for containing a pressurized medium in its interior, a bore through a wall of said container, a bar extending through said bore longitudinally thereof and reciprocable longitudinally thereof, annular sealing means encircling said bar and interposed sealingly between said bar and said wall, and piston pump means disposed inwards of said annular sealing means with respect to said interior and arranged to return to said container pressurized medium penetrating said bore to a location immediately adjacent to and inwards of said annular sealing means, said piston pump means comprising portions of said bar and said wall, a first annular non-return valve member of rectangular cross-section which closely encircles said bar, extends in said bore, is situated between said interior and said sealing means, and is formed with recesses in an annular face thereof directed towards said interior, a second annular non-return valve member which encircles said bar, bears sealingly against said wall in said bore, is situated between said interior and said sealing means, and moves with said bar on reciprocation of said bar relative to said wall, an annular groove formed in said wall co-axially with said bore, opening into said bore, and loosely receiving said first annular non-return valve member and thereby allowing said first annular non-return valve member to perform a small limited reciprocatory movement along said bore relative to said wall but otherwise preventing reciprocation of said first annular non-return valve member on reciprocation of said bar relative to said wall, means allowing said second annular non-return valve member to perform a small limited reciprocatory movement along said bar relative to said bar but otherwise ensuring that said second annular non-return valve member reciprocates with said bar, and clamping means pressing the inner periphery of said first annular non-return valve member against said bar, each of the first and second annular non-return valve members serving to prevent the medium from flowing in the direction from said interior towards said sealing means but to permit flow in the opposite direction.
 3. In combination, a container for containing a pressurized medium in its interior, a bore through a wall of said container, a bar extending through said bore longitudinally thereof and reciprocable longitudinally thereof, annular sealing means encircling said bar and interposed sealingly between said bar and said wall, and piston pump means disposed inwards of said annular sealing means with respect to said interior and arraNged to return to said container pressurized medium penetrating said bore to a location immediately adjacent to and inwards of said annular sealing means, said piston pump means comprising portions of said bar and said wall, a first annular non-return valve member which closely encircles said bar, extends in said bore, is situated between said interior and said sealing means and is substantially stationary with respect to said wall on reciprocation of said bar relative to said wall, a second annular non-return valve member of rectangular cross-section which encircles said bar, bears sealingly against said wall in said bore, is situated between said interior and said sealing means, is slit in the manner of a piston ring, and is formed with recesses in an annular face thereof directed towards said interior, means allowing said first annular non-return valve member to perform a small limited reciprocatory movement along said bore relative to said wall but otherwise preventing reciprocation of said first annular non-return valve member on reciprocation of said bar relative to said wall, and an annular groove formed in said bar co-axially with said bore opening into said bore, and loosely receiving said second annular non-return valve member and thereby allowing said second annular non-return valve member to perform a small limited reciprocatory movement along said bar relative to said bar but otherwise ensuring that said second annular non-return valve member reciprocates with said bar, each of the first and second annular non-return valve members serving to prevent the medium from flowing in the direction from said interior towards said sealing means but to permit flow in the opposite direction.
 4. In combination, a container for containing a pressurized medium in its interior, a bore through a wall of said container, a bar extending through said bore longitudinally thereof and reciprocable longitudinally thereof, annular sealing means encircling said bar and interposed sealingly between said bar and said wall, and piston pump means disposed inwards of said annular sealing means with respect to said interior and arranged to return to said container pressurized medium penetrating said bore to a location immediately adjacent to an inwards of said annular sealing means, said piston pump means comprising portions of said bar and said wall, a first annular non-return valve member which closely encircles said bar, extends in said bore, is situated between said interior and said sealing means and is substantially stationary with respect to said wall on reciprocation of said bar relative to said wall, a second annular non-return valve member of rectangular cross-section which encircles said bar, bears sealingly against said wall in said bore, is situated between said interior and said sealing means, and is formed with recesses in an annular face thereof directed towards said interior, means allowing said first annular non-return valve member to perform a small limited reciprocatory movement along said bore relative to said wall but otherwise preventing reciprocation of said first annular non-return valve member on reciprocation of said bar relative to said wall, an annular groove formed in said bar co-axially with said bore, opening into said bore, and loosely receiving said second annular non-return valve member and thereby allowing said second annular non-return valve member to perform a small limited reciprocatory movement along said bar relative to said bar but otherwise ensuring that said second annular non-return valve member reciprocates with said bar, and clamping means pressing the outer periphery of said second annular non-return valve member against said wall, each of the first and second annular non-return valve members serving to prevent the medium from flowing in the direction from said interior towards said sealing means but to permit flow in the opposite direction.
 5. In combination, a container for containing a pressurized medium in its interior, a bore through a wall oF said container, an annular groove formed in said wall co-axially with said bore and opening into said bore, a bar extending through said bore longitudinally thereof and reciprocable longitudinally thereof, a rectangular cross-section sealing ring which encircles said bar, is interposed sealingly between said bar and said wall, is loosely received in said groove, and bears against said bar and one of the side walls of the groove, clamping means pressing the inner periphery of said ring against said bar, and piston pump means disposed inwards of said annular sealing means with respect to said interior and arranged to return to said container pressurized medium penetrating said bore to a location immediately adjacent to and inwards of said annular sealing means, said piston pump means comprising portions of said bar and said wall, a first annular non-return valve member which closely encircles said bar, extends in said bore, is situated between said interior and said sealing means and is substantially stationary with respect to said wall on reciprocation of said bar relative to said wall, a second annular non-return valve member which encircles said bar, bears sealingly against said wall in said bore, is situated between said interior and said sealing means, and moves with said bar on reciprocation of said bar relative to said wall, each of the first and second annular non-return valve members serving to prevent the medium from flowing in the direction from said interior towards said sealing means but to permit flow in the opposite direction. 